Test Two Text 4

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Phases of growth can be performed with a bacterial growth curve

lag phase

log phase

stationary pahse

death phase

Lag phase

i.Lag phsase: number of cells changes very little; cells are not dormant; microbial population is undergoing a period of intense metabolic activity involving, in particular, synthesis of enzymes and various molecules

Log Phase

ii. Log phase: cells begin to divide and grow rapidly; generation time is not constant; time when cells are most active metabolically

Stationary phase

i.Stationary phase: growth rate slows and number of microbial deaths balances the number of new cells, and the population stabilizes

Death phase

i.Death phase: number of deaths exceeds number of new cells formed and population enters death phase; phase continues until population is diminished to a tiny fraction of the number of cells in the previous phase or until the population dies out entiremly

a.Direct Measurement of Microbial Growth

i.Population numbers recorded as __

ii.More commonly done in a series of __

iii.Plate counts: advantageous because it __; disadvantageous in that it __

number of cells in mL of liquid or gram of solid material

dilutions

measures number of viable cells

takes some time for visible colonies to form

1.Plate counts assume that each live bacterium can grow __

a.Plate counts are often reported as __
2.When performing this, it is important that only a __

lined in chains or as clumps

colony-forming units (CFU)

limited number of colonies develop in the plate

i.__: diluting large concentrations of bacteria to make it more feasible to read

ii.Pour Plates and Spread Plates

1.__: 1.0 mL or 0.1 mL of dilutions of bacterial suspension is introduced into a __; the nutrient medium is poured over the sample and then mixed into mediumà solidifiesà incubatedà colonies grow within nutrient agar, as well as on surface

a.Bad because some heat-sensitive microbes may be damaged; it also alters the appearance of some bacteria

Serial dilutions

Pour plate method

Petri Dish

1.__: 0.1 mL inoculum is added to the surface of a prepoured, solidified agar medium; inoculum is then spread uniformly over the surface of the medium with a specially shaped, sterilized glass, or metal rod

Spread plate method

i.__: water passed through thin membrane to filter out bacteriaà filter transferred to Petri dish

ii.__: based on the fact that the greater the number of bacteria in a sample, the more dilution is needed to reduce the density to the point at which no bacteria are left to grow in the tubes in a dilution series; most useful when microbes __

Filtration

Most Probably Number (MPN) Method

will not grow on solid media

i.__: measured volume of a bacterial suspension is placed within a defined area on a microscopic slide; afterwards, a slide is made

1.__

2.Motile bacteria are hard to count by this method; and, dead cells are counted as live onesà both are disadvantageous

a.__may occur, which may lead to a __, a term also applied to growth of a target pathogen that has developed resistance ot the antibiotic

saving valuable time

drugs destroy many normal microbes in the host

survivors to flourish and become opportunistic pathogens

Overgrowth

superinfection

a.The Action of Antimicrobial Drugs

i.They are either __(they kill microbes directly) or __(they prevent microbes from growing)

ii.In bacteriostasis, what happens?

bactericidal

bacteriostatic

the host’s own defenses usually destroy the microorganism

i.Inhibiting cell wall synthesis

1.Penicillin and certain other antibiotcs prevent the synthesis of intact peptidoglycan; the cell wall, as a result, is greatly weakened, and the cell lyses

a.Only actively growing cells are affected

i.Inhibiting protein synthesis

1.Due to structural differences in euk and pro ribosomes, eukaryotes have __ and prokaryotes have __ ribosomes

a.This difference accounts for __

i.Since mitochondria of eukaryotes also has __, they can sometimes be affected

80S

70S

selective toxicity of antibiotics that affect protein synthesis

70S

i.Injuring the plasma membrane

1.Changes in __ take place, resulting in __

ii.Inhibiting nucleic acid synthesis

1.__

the permeability

loss of important metabolites form microbial cell

DNA replication and transcription is affected

i.Inhibiting Synthesis of essential metabolites

1.Sometimes, __ can affect synthesis in that it does what?
a.Ex: PABA is a substrate for an enzymatic reaction leading to the synthesis of __, a vitamin that functions as a coenzyme for the synthesis of the purine and pyrimidine bases of nucleic acids and many amino acids

competitive inhibition

competes with the substrate for the active site, reducing the amount of product that is formed